Multiple vehicular charge sources and loads

ABSTRACT

A charge controller for a vehicle passive energy system employs an interface to a plurality of charge sources including intermittent sources, such as vehicle mounted solar photovoltaic (PV) panels and the vehicle engine and alternator, and an interface to a plurality of charge loads, such as a comfort heating ventilation, refrigeration and air conditioning (HVAC) system and auxiliary vehicle loads. Charge logic computes which of the plurality of sources will supply the charge current and which of the plurality of loads will receive the charge current, and a switch responsive to the charge logic will direct the charge current from at least one of the plurality of sources to at least one of the loads, the plurality of charge sources mutually exclusive from simultaneously powering a common load.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application No. 62/008,185, filed Jun. 5, 2014,entitled “SYSTEM AND METHOD FOR MULTIPLE CHARGE SOURCES,” and U.S.62/016,905, filed Jun. 25, 2014, entitled “SYSTEM AND METHOD FORMULTIPLE CHARGE SOURCES,” both incorporated herein by reference inentirety.

BACKGROUND

Fossil fuel alternatives have come to light in recent years as thepractical limits and eventual exhaustion of natural resources areconsidered. Tractor trailer trucks, being a leading consumer of fossilfuels and major contributor of combustion pollutants, have receivedparticular scrutiny. Further, hybrid vehicle technology, gainingincreasing popularity with smaller, consumer oriented vehicles, have yetto be adopted for larger vehicles, partially due to the limits ofgathering and storing electrical energy on a scale sufficient for suchlarger vehicles. Solar energy, however, has been viewed as a viablecontributor for ancillary vehicle loads over the native vehiclepropulsion system (i.e. diesel engine). The flat, exposed surface of atrailer roof represents untapped surfaces for solar energy ifstrategically utilized and managed.

SUMMARY

A charge manager and controller for a vehicle passive energy systememploys an interface to a plurality of charge sources includingintermittent sources, such as vehicle mounted solar photovoltaic (PV)panels and the vehicle engine and alternator, and an interface to aplurality of charge loads, such as a comfort heating/ventilation,refrigeration systems and auxiliary vehicle loads. Charge logic computeswhich of the plurality of sources will supply the charge current andwhich of the plurality of loads will receive the charge current, and aswitch responsive to the charge logic will direct the charge currentfrom at least one of the plurality of sources to at least one of theloads, in which the plurality of charge sources may be mutuallyexclusive from simultaneously powering a common load due to differingelectrical characteristics required by the load.

In the example configuration herein, the system for switching electricalsources in the vehicle electrical system includes a native vehicleelectrical source and a passive electrical source, including chargelogic for identifying differing electrical characteristics between afirst power source and a second power source, and a controller forconverting power corresponding to the electrical characteristics of thefirst power source to correspond to the characteristics of the secondpower source for charging the second storage element from the firstpower source. A switch in the controller is responsive to the chargelogic for switching the converted power to the second storage element,such that unmatched power sources defined by differing electricalcharacteristics maintain electrical separation, to avoid commonconnection of dissimilar voltages. Therefore, the switch may permitshared or cross charging between the native vehicle and trailer(auxiliary) power systems while the sources remain mutually exclusive ofsimultaneously powering a common load.

Configurations herein are based, in part, on the observation that thevehicle alternator often exceeds the demands of storing electricalenergy sufficient to operate the starter and other native loads such asheadlights and fuel pumps/injectors. In effect, the alternator istypically capable of overcharging the starting battery, particularly onlong trips where the engine is running long distances between starts. Amodulator or regulator, such as a pulse width modulator (PWM), controlsthe charge current to the battery to avoid overcharging, howeverconventional approaches do not leverage this untapped source ofpotential electrical power.

Unfortunately, conventional approaches to vehicle based electricalenergy management operate separate vehicle (tractor) and trailer (cargostorage) power systems. Conventional trailer loads, such as reefers,require a dedicated combustion engine and/or generator combination, andcannot benefit from potential excesses of the tractor engine alternator.Further, conventional trailers suffer from the shortcoming that they donot employ available passive energy sources such as roof mounted solarpanels or regenerative brakes. Excess solar energy can be stored andutilized by the propulsion power system for powering non-essential loadssuch as comfort stations, rather than operating the propulsion enginesolely for the electrical powering of the comfort station, such as asleeper cab HVAC system. Accordingly, configurations hereinsubstantially overcome the above described shortcomings by providing adual charging approach where the propulsion power system and theauxiliary power system of the trailer can offset power (battery)exhaustion by transferring electrical power between the power systemsusing a smart switch to interconnect and share power by accommodatingthe differing electrical characteristics between the charging systems.

An auxiliary power source, such as a solar photovoltaic (PV) array,produces energy for non-propulsion auxiliary electrical loads andrecharge auxiliary batteries. These auxiliary loads are supported by thepropulsion power system (i.e., engine/alternator) during periods ofunderproduction if the propulsion system is on. When the propulsionsystem is not operating, the auxiliary loads are supported by anauxiliary battery system. Energy from the auxiliary power source is usedto recharge the auxiliary battery system. In the case of a solar powersource, a Maximum Power Point Tracking (MPPT) charging system wouldcontrol the solar operating point at a voltage greater than theauxiliary battery voltage and charge the auxiliary battery using acombination of maximum current and controlled voltage algorithms.Alternatively, other mechanisms may be employed for adjusting chargevoltages when the solar sources and vehicle sources have differingmaximum voltages (i.e. 12v and 24/48v). This battery-charging scenariominimizes battery stress and overheating to achieve long-term batterylifetimes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a context diagram of a vehicle suitable for use with thecharging system as disclosed herein for a solar auxiliary power system(APS) application; and

FIG. 2 is a block diagram of a charging system in the vehicle of FIG. 1;

FIG. 3 shows a functional diagram of charge current flow in anintegrated PWM (Pulse Width Modulation) and solar MPPT chargingapplication; and

FIG. 4 is a flowchart of charge logic in the auxiliary power system ofFIG. 3

DETAILED DESCRIPTION

The current trend to conserve fossil fuel through less engine idling andthe addition of an APS to support non-propulsive electrical loads in thetransportation industry is well established. However, there remains asynergistic problem with the conservation of energy, especially for asolar power system application where the marginal power output isessentially free but intermittent. Modern propulsion systems includefull time parasitic electrical loads and these loads (e.g. vehicleelectronics, GPS and monitoring systems) will drain a primary battery(typically a vehicle starting battery) while the propulsion system isoff. In many cases, a primary battery can be depleted in less than twoweeks. When the propulsion system is on, the alternator supports thepropulsion electrical load and charges the primary battery using aconstant voltage PWM charging scheme.

FIG. 1 is a context diagram of a vehicle suitable for use with thecharging system as disclosed herein for a solar auxiliary power system(APS) application. Referring to FIG. 1, in a transport environment 100,a transport vehicle 110 such as a class 8 truck has a trailer 112 orother cargo area 112′. The trailer has a reefer (refrigerator)fan/compressor 120-1, liftgate 120-2, or other loads 120 (generally). Astorage element such as a battery bank 120-99 stores power and is also aload 120 responsive to charging. The trailer loads 120 are generallyfocused on cargo transport and related demands.

The transport vehicle 110 employs a propulsion system (diesel engine)and a propulsion power system for powering native vehicle electricalloads, most notable a starter motor 130-1 for starting the dieselengine. The propulsion power system includes an alternator 132 forpowering the propulsion vehicle loads such as the battery 130-99 andother loads 130 generally such as a comfort station (HVAC), lights,radio and cab communication systems. Various configurations andcombinations of loads may be envisioned. If cooling demand allows,electrical energy may be employed to cool the reefer area of the trailer112. The cab comfort station, common on long haul trucks for augmentinga sleeper cab arrangement, employs electrical power for HVAC functions,as well as entertainment and food preparation.

FIG. 2 is a block diagram of a charging system in the vehicle of FIG. 1.Referring to FIGS. 1 and 2, the trailer, or cargo, loads 120 are poweredby an auxiliary power system 122 separate from the propulsion powersystem 134. The auxiliary power system 122 receives power from a passivesource such as solar panels 140 disposed on the roof of the trailer 112.Through configurations discussed further below, the propulsion powersystem 132 and auxiliary power system 122 exchange excess power foravoiding a power shortfall, for example on a cloudy day when the solarpanels 140 are challenged but the vehicle 110 is traveling at highwayspeed and the alternator 132 is generating ample power.

The propulsion power system 134 is generally defined by the nativevehicle charging and starting system on the vehicle 110, typically 12v.Since the alternator 132 often experiences substantial periods oflimited draw, excess electrical power (energy) diverts to the auxiliarypower system 122. The reverse may also be performed where excess solargenerated power, stored in the batteries 120-99, may power the comfortstation or other loads during stationary vehicle periods.

The auxiliary power system 122 includes the solar array 140 mounted onthe roof of the trailer 112, and connects to an MPPT charger 142 forstoring and distributing the solar generated power. The MPPT charger 142directs and controls the solar panels for delivering a maximum voltagefor charging. Generally, the propulsion power system 134 and theauxiliary power system 122 have different voltage characteristics. Aprogrammable smart switch, or controller 150, converts electricalcharacteristics (current and voltage) to correspond to the trailer load120 or the propulsion load 130, as determined by alternator charge logic138 and solar charge logic 128. As depicted, the charge controller 160includes the MPPT charger 142, the PSS 150 for directing and convertingvoltage using PWM (Pulse width modulation) and/or rectification, andalternator 138 and solar 128 charge logic for directing current to therespective batteries without overcharging and to promote batterylongevity. In a typical configuration, the propulsion power system 134operates on 12v and the auxiliary power system 122 employs the solarpanel generation 140 between 12v and 48v. Dynamic switching andconfiguration of the solar panels 140 is discussed further in copendingU.S. patent application Ser. No. 13/752,765, filed Jan. 29, 2013,entitled “METHOD AND APPARATUS FOR VEHICULAR ENERGY MANAGEMENT,”incorporated herein by reference.

Voltage characteristics of the respective propulsion 134 and auxiliary122 power systems include different voltages, as well as differentcharging patterns. The programmable smart switch 150 employstransformers and modulations to modify voltage to be consistent with thesystem 122, 134 being powered or charged (recall that the batteries120-99 and 130-99 are also a load in the respective system). Electricalcharacteristics include current, voltage, and AC/DC. Generally, voltagesshould be substantially similar for cooperation between the differencesystems. Charge voltages are typically about 10-20% higher than thedemand voltage of the system they support, however different chargelogic varies. Alternators, by definition, generate an AC signal, howeverthis is rectified or modulated to DC at the alternator before enteringthe propulsion power system 132, which corresponds to the DC signalderived from the solar panels 140. The charge manager 160 orprogrammable smart switch 150, therefore, needs to transform the voltageto produce a current that is compatible to charge or supply loads of thedemand system 122 or 134.

When both propulsion and auxiliary battery-charging systems areoperational (such as during daylight driving for solar applications),they are mutually exclusive because of the difference in chargemanagement schemes, e.g., PWM versus MPPT. The auxiliary charging systemtypically cannot support an active PWM system with excess auxiliarypower using the standard charging algorithm. If it were possible, thenexcess auxiliary energy (power not needed to charge auxiliary batteries)would not only offset the primary battery charging requirement butwould—by working in unison with the propulsion PWM system—offset thetotal electrical load to the extent of the excess auxiliary energy.Utilizing excess auxiliary energy in the propulsion electrical systemoffsets the alternator load and results in conservation of fuel andlowers operating costs.

FIG. 3 shows a Functional Diagram of charge current flow in anintegrated PWM (Pulse Width Modulation) and solar MPPT chargingapplication. The introduction of the Programmable Smart Switch (PSS),150 included in the charge manager 160 shown in FIG. 3, will allow thetwo separate charging systems to employ excess energy while either orboth systems are operating at the same time. Proper batterystate-of-charge can be managed through automatic propulsion startupoption and prolonged propulsion down time does not result in a depletedbattery charge state. Excess energy from the APS is fully utilized,which can reduce fuel consumption and propulsion system maintenancecosts.

In the general framework outlined herein, each of the charge loads has acorresponding charge source, and the charge logic is operable todetermine if a charge load is satisfied, and directs the charge currentfrom the charge source of the satisfied load to one of the other chargeloads. For example, in a typical vehicle, the loads include a primaryload, such that the primary load takes precedence to other loads forreceiving charge current, and powers critical loads such as vehicleelectronics. The charge source includes the native vehicle alternator(e.g., 12V) charging system and primary battery. The loads also includeauxiliary consumers, such that the auxiliary consumers have intermittentand non-immediate needs for receiving charge current, for example acomfort HVAC system, refrigeration unit or liftgate with correspondingauxiliary battery system. Accordingly, the charge sources include anon-demand source and an intermittent source.

In the typical configuration, the auxiliary consumers such as comfortHVAC, refrigeration, or liftgate systems draw power first from the APS(e.g., solar PV panels and corresponding storage batteries), which isseparate from the vehicle propulsion power system (the primary powersystem). The plurality of sources can include a PWM source and a MPPTsource, where the PWM source can be a rotary powered alternator 132 andthe MPPT source can be a solar system 140. Also, the on-demand sourcecan be an internal combustion engine having an independent fuel source,and the intermittent source can be a solar PV panel, thus giving rise tothe mutually exclusive charging mechanisms that the present approachseeks to interoperate.

In a particular configuration, the charge manager 160 includes acombination of a modified MPPT charger 142 and a separate programmablelogic matrix that controls the energy flow between the APS and thepropulsion power system. The PSS 150 uses various real time analogparameters and ampere-hour algorithms to manage battery state of charge(SOC) and battery operating voltage. An operator sets system operatinglimits (e.g., voltage and temperature) at installation, and also batteryoperating limits (e.g., ampere-hour capacities) to control and achievemaximum system efficiency for different battery chemistries.Alternatively, automated default or turnkey startup parameters may beprovided with the option to override or modify.

Power management and battery charging are prioritized by the PSS 150through sequencing by first directing all APS 122 energy to theauxiliary loads 120 and the auxiliary battery 120-99. Auxiliary loadsare typically satisfied first since they are designed to be independentof the propulsion power system to conserve fuel consumption. Once theauxiliary power demand is satisfied, the PSS will direct excess energyfrom the APS to the propulsion power system using a modification of theAPS charger to interface with the constant voltage primary electricalsystem while maintaining peak power tracking of the available solarenergy.

Nighttime operation is also controlled by the PSS 150 through monitoringof the auxiliary battery 120-99 SOC. The auxiliary battery is the primesource of nighttime energy for auxiliary loads until a predetermined lowSOC is detected. At that time the PSS 150 will redirect the propulsionpower system 132 to support the auxiliary load through a set of logicswitches until the load demand is satisfied including partial auxiliarybattery recharge. If the propulsion power system is off, then the PSS150 will start the propulsion power system 134 and then turn it off whenthe power management conditions are met, also known as auto-startcapability. Thus, charge logic is operable to initiate the on-demandsource if the auxiliary battery has an insufficient SOC.

The PSS is continuously monitoring both power systems operational statusand auxiliary and primary battery charge states. During long, daylightnon-powered idle periods 134, the PSS supports the primary systemparasitic loads with solar power and maintains both the auxiliary andprimary battery systems at a full SOC. Proper and constant batterycharge management coupled with power management results in loweroperational costs and prevents unplanned downtime due to reduced SOC.

In an implementation vehicle using such a system, consider that eachbattery is a load. These loads are in parallel with the power source andeach power source circuit is separate with its own charge controllermanaging the voltage. At any one time these two power circuits are atdifferent voltages. When we try to put each power circuit in parallel sothat the one with extra power can contribute to the other, the chargecontrollers may become confused because the combined voltages will bedriven to the same level per basic principles according to Ohm's Law.

This scenario identifies where the PSS 150 imbedded charge controller(or other suitable control logic) takes over while still being able todrive the solar array power source at the maximum power point. Thecharge manager 160 can sense the voltage state of each circuit andcontrol the current distribution at the separate circuit voltage leveleven though these voltages are constantly changing do to other loadinfluences in parallel with the separate batteries, i.e. Auxiliary HVACcycling, lift gate operation or a primary load like wipers, turn signalsor even an electrical clutch on the engine air conditioner cycling.

If the auxiliary battery voltage is 1 to 1.5 volts lower when theprimary power source is connected to the auxiliary circuit, the higheralternator reference voltage will force both circuits to seek the highervoltage since it is the stronger element and the auxiliary MPPT charger142 will essentially shut down with the loss of the solar power. The PSS150 manages these voltage differences so that all of the available solarpower is utilized for both power circuits at the same time, thusreducing demand on the alternator and subsequently fuel consumption. Ofcourse at night the PSS uses the alternator to support the auxiliarycircuit when the auxiliary battery is near depletion.

Configurations disclosed herein perform management of the differingvoltages of the primary and auxiliary systems and managing twoparalleled separate power sources with independent battery loadcontrollers to continue to utilize the MPPT function of one of thecharge controllers. Contributing loads are in parallel across the powersources and, an integration of two separate power circuits in parallelmay cause undesired operation without the PSS logic controller foridentifying and directing current flow in conjunction with varyingvoltage sources.

A system operator, such as a driver or maintenance personnel, may chooseto set the propulsion system as the principal power source if conditions(e.g., weather) or operational timing suggest that the system operationwould be more effective. In this scenario, the PSS uses a combination ofthe propulsion and auxiliary power to meet all load demands includingauxiliary battery recharge. If the system is operating when the both thepropulsion power system and APS are under producing (e.g., night restperiod), the PSS will use power from the primary battery until theprimary battery drops to a preselected SOC. At that time the primarybattery is disconnected and the auxiliary battery assumes all loaddemand until it reaches a preselected SOC. When both battery systems areat a preselected lower SOC, then the PSS starts the propulsion system toprovide alternator power for the loads and to begin battery rechargeuntil a new, higher logic point SOC is achieved. The battery dischargecycle then repeats.

If the charge controller is operating when the APS is producingsufficient power (e.g., solar system in a daylight environment), thecycle logic is the same except when the load demand is satisfied orremoved, the APS will support battery maintenance charging without theneed for propulsion power.

Referring to FIG. 1, in an example configuration, a vehicle chargemanagement system including the disclosed charge controller provides thefollowing advantages:

-   -   Charge energy management between two (or more) different power        sources and battery charge management systems;    -   Automatically maintains battery SOC during long storage periods        for each power system;    -   Prioritizes energy utilization;    -   Maximizes use of all excess APS energy for battery charging and        offsetting load demands;    -   Reduces fuel consumption;    -   Versatile operation through user defined operating parameters        and battery chemistry;    -   Continuous battery SOC monitoring and charge maintenance during        primary power system non-operational periods; and    -   Helps prevent unplanned loss of power system operation.

Functional diagrams of an integrated Primary Power System PWM and solarAPS MPPT charging system are shown in FIGS. 2 and 3. Referring to FIGS.2 and 3, the PSS 150 is integrated into the MPPT Solar Charge Chargemanager 160 to allow for seamless sharing of solar energy between twodifferent battery charge management systems while forcing the solarpower source (array) 140 to operate at a maximum power operating point.The PSS 150 senses both battery system voltages, i.e., V_(AB) (11) andV_(PB) (3), and solar power voltage to establish a power distributionrequirement, and then the PSS 150 manages the amount of battery chargecurrent, i.e., I_(AB) and I_(PB), to control battery SOCs. The auxiliarybattery 120-99, charging through the Solar Charge Logic 128, interfaceuses a well-defined, industry based battery charge profile scheme ofcharging to a controlled maximum voltage followed by a constant voltagecharge period and then a maintenance charge to prevent self-discharge.Maximum battery energy utilization and extended cycle life are achievedwith this battery-charging scenario.

When the PSS 150 senses that the APS has excess power, it will divertcurrent, i.e., I_(S) (4) over interconnection 170 through the alternatorcharge logic 138 while maintaining load and battery charging support tothe APS. The alternator charge logic 138 modifies and controls theexcess solar power to operate at the alternator 132 with Imbedded PWMcontrol voltage, i.e., V_(PA), to deliver load current, i.e., I_(PL),and primary battery 130-99 current, i.e., I_(PB), to the primary powersystem 134. In this approach, charge logic is configured to transfercharge current to the vehicle/alternator system by direct charge currentfrom the intermittent source to the auxiliary consumers and determinethat the auxiliary consumers and the corresponding battery aresatisfied. The charge charge manager 160 converts the excess chargecurrent into a form expected by the primary load 130 to accommodate thedifferences between the PWM and MPPT signals, and directs the chargecurrent from the intermittent (auxiliary) source 140 to the primary load130 and corresponding battery 130-99.

Power distribution between the two different power systems is also shownin the Functional Diagram of FIG. 3. The propulsion system alternator132 with Imbedded PWM provides current at a fixed voltage, i.e., V_(PA),to the propulsion system load 130 and the primary battery 130-99 whilethe propulsion system 134 is operating either in an idle state or on thehighway at a higher engine rpm. When the primary battery 130-99 reachesa full SOC, the PWM charge controller, integral to the engine alternator132, will reduce battery charge current to prevent an unwantedovervoltage condition. The PWM will control all current flow using afixed, factory preset, voltage reference, i.e., V_(PA). If the SOCconditions in the APS as defined by the PSS require external load/chargepower support, then the PSS will set Alternator Charge Logic to passcurrent, i.e., I_(S) into the APS using the voltage control reference ofthe PWM regulator.

In this manner, the charge manager 160 identifies when a primary load issatisfied from a primary source, and identifies electricalcharacteristics of an auxiliary load. The controller then convertsexcess power from the primary source to correspond to the identifiedelectrical characteristics. In the example configuration employing atractor trailertransport vehicle, the primary load is s battery and issatisfied upon achieving a maximum state of charge (SOC).

Therefore, the charge logic is further configured to transfer chargecurrent to the auxiliary loads 120 by directing charge current from theon-demand source to the primary load and detect an overvoltage conditionpending due to a SOC of the battery corresponding to the primary load.The charge logic determines if the auxiliary load has a SOC forabsorbing charge current, and directs charge current from the on-demandsource to the auxiliary consumers. Further, in configurations herein,the charge logic is operable to initiate the on-demand source if thebattery has an insufficient SOC. In other words, the charge controllercan start the primary system to initiate the on-demand charge source ifthe auxiliary source (battery) supporting an auxiliary load depleted,e.g., refrigeration unit is dying, thus preventing cargo spoilage.

FIG. 4 is a flowchart of one example of charge logic in the auxiliarypower system of FIG. 3. It should be emphasized that configurationsherein are directed to establishing and maintain a priority of loads ofdifferent electrical characteristics to permit receiving a voltage andcurrent corresponding to a first voltage characteristic and output aconverted voltage and current corresponding to a second voltagecharacteristic, and that the disclosed flowchart is one particularapproach that may be employed to accomplish this end. Referring to FIGS.3 and 4, at step 200 identifying voltage characteristics of a vehicleprimary load, in which the primary load includes a storage element orbattery operable for starting the vehicle. The primary load is operableto be powered by the propulsion power system 134, and includes thevehicle starter 130-1. The controller 142 identifies voltagecharacteristics of an auxiliary source provided by an auxiliary powersystem, in which the auxiliary power system 122 includes at least onepassive source such as solar panels 140, as depicted at step 202. ThePSS 150 enters a control loop to poll or check the auxiliary systems andidentify if switching charge capacity is appropriate. A check isperformed, at step 204, to determine if the vehicle primary loads aresatisfied. The primary loads include the starting battery, and otherloads such as lights and fuel pumps employed for vehicle propulsion. Ifthe primary loads 130 are satisfied, a further check is performed, atstep 206, to identify if the auxiliary loads 120 are satisfied.

If the primary load is not satisfied, such as a weakening startingbattery from operating a comfort station, then a check is performed, atstep 208, to determine if excess power is available from the auxiliarypower system 122. If so, the PSS 150 converts, if a primary load is notsatisfied and an auxiliary source has available excess power, theelectrical characteristics of the available excess power to correspondto the primary load, as depicted at step 210, and directs the convertedexcess power to the primary load, as shown at step 212, to bring theprimary battery 130-99 back to full charge.

If excess power is not available, then a check is performed, at step214, to determine if the voltage of the primary battery 130-99 is belowminimum. If so, then the propulsion power system commences the primarysource by starting the diesel engine to invoke the alternator 132, asdepicted at step 216. It is generally preferable to employ the dieselengine as a fallback for use only when other sources (i.e. shore power,auxiliary power) have been exhausted.

If, at step 206, the auxiliary load is not satisfied, such asinsufficient comfort station HVAC performance, then the PSS 150 checksto see if there is excess power available in the propulsion powersystem, as shown at step 218. The controller converts, if an auxiliaryload is not satisfied and a primary source has available excess power,the electrical characteristics of the available excess power tocorrespond to the auxiliary load, as shown at step 220, and directingthe converted excess power to the auxiliary load, as disclosed at step222. Note that this may subsequently result in starting the dieselengine at step 216 to effectively allow the vehicle alternator 132 topower the reefer load and avoid cargo loss.

If the propulsion power system 134 does not have available excess, thena check is performed, at step 224, to determine if the auxiliary voltageis below a minimum. If so, then the controller mitigates the auxiliaryload, as depicted at step 226, by shutdown of loads 120 or commencingthe primary source as described above, if possible.

The charge logic maintains a state of charge of each battery bydirecting the charge current to a controlled maximum, followed by aconstant charge, and followed by a maintenance charge sufficient toprevent charge depletion of each battery.

Power management is achieved using an ampere-hour counting system aspart of the PSS 150 controlling logic. Both charge and dischargecurrents, I_(AB) and I_(PB) are measured and time logged. Minimum SOCreferences are compared to real time battery SOCs. If a minimum SOCreference is met, then the PSS will take action to reduce the affectedbattery load, remove the affected battery load or redirect availablePrimary or APS energy to prevent further battery energy losses.

The PSS integrated MPPT Solar Charge Controller is capable of seamlesslysharing excess solar energy between two different battery chargingcontrol systems. Using specialized control logic schemes and energymanagement logic, both power system battery energy states are maintainedand controlled for maximum energy utilization and minimal lifecyclestress. Operational efficiencies are achieved through fuel conservationwhile user interface logic options maximize versatility and simplicity.

While the system and apparatus has been particularly shown and describedwith references to embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention encompassed bythe appended claims.

What is claimed is:
 1. In a vehicle electrical system including at leastone passive source and a primary load, a method of maintaining vehicleelectrical loads, comprising: identifying voltage characteristics of avehicle primary load, the primary load including a storage elementoperable for starting the vehicle; identifying voltage characteristicsof an auxiliary source provided by an auxiliary power system, theauxiliary power system including at least one passive source;converting, if an auxiliary load is not satisfied and a primary sourcehas available excess power, the electrical characteristics of theavailable excess power to correspond to the auxiliary load; anddirecting the converted excess power to the auxiliary load.
 2. Themethod of claim 1 further comprising: converting, if a primary load isnot satisfied and an auxiliary source has available excess power, theelectrical characteristics of the available excess power to correspondto the primary load; and directing the converted excess power to theprimary load.
 3. The method of claim 1 further comprising identifyingwhen a primary load is satisfied from a primary source; identifyingelectrical characteristics of an auxiliary load; converting excess powerfrom the primary source to correspond to the identified electricalcharacteristics.
 4. The method of claim 3 wherein the primary load is sbattery and is satisfied upon achieving a maximum state of charge (SOC).5. A charge controller comprising: an interface to a plurality of chargesources; an interface to a plurality of charge loads; charge logic forcomputing which of the plurality of sources to supply the charge currentand which of the plurality of loads receive the charge current; and aswitch responsive to the charge logic for directing the charge currentfrom at least one of the plurality of sources to at least one of theplurality of loads, the plurality of charge sources having differentvoltage characteristics for powering a common load.
 6. The controller ofclaim 5 wherein each of the charge loads has a corresponding chargesource, and the charge logic is operable to: determine if a charge loadis satisfied; and direct the charge current from the charge source ofthe satisfied load to one of the other charge loads of the plurality ofcharge loads.
 7. The controller of claim 6 wherein the charge sourcesinclude an on-demand source and an intermittent source, and each of thecharge loads include a corresponding battery.
 8. The controller of claim7 wherein the charge logic is operable to initiate the on-demand sourceif the battery has an insufficient state of charge (SOC).
 9. Thecontroller of claim 8 wherein the on-demand source is an internalcombustion engine having an independent fuel source, and theintermittent source is a solar PV panel.
 10. The controller of claim 8wherein the charge logic maintains a SOC of the battery by directing thecharge current to a controlled maximum, followed by a constant charge,and followed by a maintenance charge sufficient to prevent chargedepletion of the battery.
 11. The controller of claim 6 wherein theplurality of loads includes a primary load, the primary load takingprecedence to other loads for receiving charge.
 12. The controller ofclaim 11 wherein the loads include auxiliary consumers, the auxiliaryconsumers having intermittent and non-immediate needs for receivingcharge current.
 13. The controller of claim 12 wherein the charge logicis configured to: direct charge current from the intermittent source tothe auxiliary consumers; determine that the auxiliary consumers and thecorresponding battery are satisfied; convert the charge voltage into aform expected by the primary load; and direct the charge current fromthe intermittent source to the primary load and corresponding battery.14. The controller of claim 12 wherein the charge logic is configuredto: direct charge current from the on-demand source to the primary load;detect an overvoltage condition pending due to a SOC of the batterycorresponding to the primary load; determine if the auxiliary load has aSOC for absorbing charge current; convert the charge voltage into a formexpected by the auxiliary load; and direct charge current from theon-demand source to the auxiliary consumers.
 15. The controller of claim11 wherein the auxiliary load includes a refrigeration system forperishable cargo.
 16. The controller of claim 5 wherein the plurality ofsources include a PWM (Pulse Width Modulated) source and an MPPT(Maximum Power Point Tracking) source.
 17. The controller of claim 5wherein the PWM source is a rotary powered alternator and the MPPTsource is a solar panel.
 18. A system for switching electrical sourcesin a vehicle electrical system having a native electrical source and apassive electrical source, comprising: charge logic for identifyingdiffering electrical characteristics between a first power source and asecond power sources; a controller for converting power corresponding toelectrical characteristics of the first power source to correspond toelectrical characteristics of the second power source for charging thesecond storage element from the first power source; a switch responsiveto the charge logic for switching the converted power to the secondstorage element such that unmatched power sources defined by differingelectrical characteristics maintain electrical separation.
 19. Thesystem of claim 18 wherein the first power source and second powersource are mutually exclusive of simultaneously powering a common load.20. The system of claim 19 wherein the controller includes aprogrammable smart switch adapted to receive a voltage and currentcorresponding to a first voltage characteristic and output a convertedvoltage and current corresponding to a second voltage characteristic.